What characteristic defines all microbes?

The defining characteristic that sets all microbes apart is their microscopic size. Microbes, which include bacteria, viruses, fungi, and protozoa, are typically not visible to the naked eye and can only be observed under a microscope. This characteristic is crucial in distinguishing microbes from larger organisms, such as plants and animals.

Multicellular organisms, on the other hand, comprise multiple cells and do not fit the microbial definition, as many microbes are unicellular (single-celled). The visibility of organisms to the naked eye varies widely; larger organisms are easily seen without magnification, while microbes require microscopic observation due to their small size. Lastly, while some microbes can indeed be harmful to humans, many are beneficial and essential for processes such as digestion and decomposition. Thus, the notion that all microbes are harmful is inaccurate and further emphasizes the importance of understanding their microscopic nature as the defining characteristic.